1. Field of the Invention
The present invention relates to an enhanced power-saving mechanism in an IEEE 802.16e system, and more particularly, to a scheduled power-saving method in an IEEE 802.16e system that improves power-saving performance by extending an unavailable state of a mobile station when two or more service connections in the mobile station are switched to a sleep mode.
2. Discussion of Related Art
IEEE 802.16 defines four service classes to guarantee quality of service (QoS). These are unsolicited grant service (UGS), real-time polling service (rtPS), non-real-time polling service (nrtPS), and best effort service (BES).
A UGS connection should have a higher priority than the other service connections. In the UGS connection, there is no explicit bandwidth request from respective mobile stations (MSs), such as cell phones. Each base station (BS) must periodically guarantee a bandwidth as much as a fixed data size for the UGS connection. UGS is used for applications having a constant bit rate (CBR) characteristic, such as Voice over IP (VoIP) or video conference.
In general, rtPS and nrtPS connections are polled by a unicast polling request. The rtPS takes polling that causes no network congestion or satisfies a delay requirement for a service flow. On the other hand, the ntPS connection takes less polling than when a network congests or operates on a competition basis. That is, since the rtPS takes polling that causes no network congestion or satisfies a delay requirement for a service flow, it is protected from competition-based requests and used for real-time VBR streaming service, such as NPEG video. On the other hand, nrtPS and BES, that are insensitive to packet loss or real time, are used for non-real-time connections.
There are two types of WiMAXs: IEEE 802.16-2004 (or 802.16d) called fixed WiMAX and IEEE 802.16e called mobile WiMAX. The greatest difference between the two profiles is in mobility support, as can be seen from their names. IEEE 802.16e supports mobility while IEEE 802.16-2004 does not support mobility.
IEEE 802.16e supports handover between base stations to guarantee mobility. Another advantage of IEEE 802.16e is that it is IP-based technology. This advantage is great in that as future mobile stations develop toward 4G, all techniques will be shifted into all-IP based techniques.
IEEE 802.16e is attracting attention as technology supporting next-generation mobile networks, and positions itself as a broadband wireless access system for providing long-distance transmission and fast multimedia service in order to replace expensive wired systems due to such advantages.
In the IEEE 802.16e system, battery-driven mobile stations require a power saving mechanism to guarantee mobility by overcoming a limited amount of power.
The IEEE 802.16e system basically simultaneously supports several service connections. Each service connection performs a unique operation depending on applications. Then, several service connections may simultaneously switch to a sleep mode. According to a standard power-saving mechanism, when one service connection is in a sleep state and the other service connection is in a listening state, a mobile station moves to an available state and consumes power.
As such, when several service connections simultaneously switch to a sleep mode, a situation in which one service connection is in a sleep state and the other is in a listening state occurs frequently. A conventional technique cannot properly cope with this situation, and thus the mobile station moves to an available state and consumes power, reducing a lifetime of a battery.